A wealthy Pfizer exec is waging an “unbearable” battle to get custody of his girlfriend’s 6-month-old son, after the child was taken into state custody in the wake of her suicide on New Years Day, according to court documents.

Child welfare officials took little Lincoln, from Jonathan Sporn — even though he and the mom were raising the boy as his own — because he is not the tot’s biological father.

Yesterday he edged a step closer to a reunion, as a Manhattan judge ruled he must undergo home visits before getting custody.

“I respectfully submit that the heartbreak and searing pain that I feel as a result of this loss is nearly unbearable,” the dad said in an affidavit, citing both his partner’s death and the separation from his son.

Sporn lived with his son Lincoln’s mom, corporate attorney Leann Leutner, 40, at his Riverside Drive apartment for over two years.

They couldn’t conceive naturally and Leutner had in-vitro fertilization with an anonymous sperm donor, the documents explain. The two never married but Sporn submitted to the court a document appointing Sporn the guardian of their child as evidence. Leutner killed herself in late December at an apartment in New Jersey.

The devastated dad’s next court date is Jan. 29.

“I am begging this Court to assist me in piecing together the shattered pieces of my heart,” he pleaded.